The present invention relates to a pressure controlled fluid pressure extrusion method. The term “fluid pressure extrusion method” defines a method in which extrusion is conducted under the action of fluid pressure. Pressure control describes the adjustment of this fluid pressure in order to conduct proper extrusion. These extrusions can be used to make parts for automobiles such as helical gears and the like.
Examples of the prior art include forward extrusion methods as shown in FIG. 1 of Japanese Laid-Open Patent Publication Number 11-254082 and FIG. 3 of Japanese Laid Open Patent Publication Number 7-308729.
Referring to FIGS. 3(A)-3(D), the essentials of these prior art methods are schematically shown in order to compare these methods of the prior art with the present invention. A material 11 progresses through the steps of 3(A), 3(B), 3(C), and 3(D) to produce a manufactured product 15. Because the example of product 15 is perforated, material 11 is also perforated and a mandrel present in the metal mold.
Referring to FIG. 3(A), the outer diameter of material 11 is approximately the same size as the inner diameter of a container 12b. Referring to FIG. 3(C), when material 11 is extruded into a die 12 and molded by a punch 13, a large frictional force is generated between the material outer diameter and the container. Furthermore, when molding helical gear part 15a of manufactured product 15 with a helical gear part 12a of die 12, product 15 rotates as it advances along a lead. This rotation adds a large additional frictional force in the direction of rotation as well as the frictional force in the axial direction as described above. As a result, the load needed for working is increased, and there are negative effects on the product precision and on the die life. With this method, the outer diameter part of the material must be straight. If the outer diameter is tiered, the smaller diameter part could become deformed and expand during molding, and the specified molding cannot be conducted.